Mildly built 5.0 misfire

LaserRed · Jan 3, 2013

Hey guys I use to have a user name on here but apparently it doesn't work anymore so I made a new name.

i Have a 95 Gt that is mildly built (HCI).

When I first initially start up the car it revs up and down( im assuming the iac is bad) and it has a horrible miss until it warms up. Then the miss is only noticeable in the lower rpms particularly when I change gears and first touch the throttle. When I'm at WOT it the car doesn't miss, but it doesn't feel as fast as it used to.

I have changed the plugs, wires, cap and rotor both 02 sensors with no luck. Also I feel I should mention the car has blow by issues ( 130,000 mile short block with new hci) I know I should of had the bottom end redone but I was on a budget. Oil does get up into the intake and I have to clean it out every so often and at it's worst I've seen oil get into the actual CAI and down near the Mass air flow sensor. I would try changing the mass air flow sensor but im not sure if that would effect my dyno tune ( Car has 30lb injectors with the stock mass and was tuned by Dave guy.)

Any and all help is appreciated guys I really wanna get this thing running right again. Makes me sad to see it sit all the time. Thanks in advance guys!

CC'S95GT · Jan 3, 2013

ck the TPS for dead spots.
Connect the ohm meter to any 2 of the wires on the TPS and very slowly turn the throttle while watching the ohms increase. your looking for any drops or jumps in the resistance.

LaserRed · Jan 4, 2013

When I get a chance I will do so, if I do see any drops does that mean the tps is bad?

Edit: And should I do this as soon as I start the car up or should I let it warm up first?

SL0WNESS · Jan 4, 2013

check tps voltage with KOEO (key on engine off..)

what plugs are you using?

CC'S95GT · Jan 4, 2013

LaserRed said:
When I get a chance I will do so, if I do see any drops does that mean the tps is bad?

Edit: And should I do this as soon as I start the car up or should I let it warm up first?

Resistance ck should be done with the car off and connector unplugged. sorry.
It can be done with KOEO (key on engine off) but with the meter setting on VDC. I would prefer the previous.
An analog meter is prefered for this test but it can be done with a digital but the throttle movement needs to be very slow.
Any drops in resistance or voltage (depending of what method your using), would indicate a breakdown in the TPS.
The TPS is a rheostat. (like a dimmer sw on your lights).

ProKiller · Jan 4, 2013

have you checked your engine/chassis ground? also just clean out the maf first before replacing it. i'm really surprised he was able to get a tune to work with a stock maf and 30# inj.

94Snake · Jan 4, 2013

ProKiller said:
. i'm really surprised he was able to get a tune to work with a stock maf and 30# inj.

ok please help me understand why it would be hard to tune a stock MAF with 30 lb injectors? I'm not looking to shoot this down, i just want to know.

LaserRed · Jan 4, 2013

ProKiller said:
have you checked your engine/chassis ground? also just clean out the maf first before replacing it. i'm really surprised he was able to get a tune to work with a stock maf and 30# inj.

When he first tuned it the car ran perfect in every way. As well he told me it's actually easier to tune the stock maf then it is an aftermarket one. But who knows.

toyman · Jan 5, 2013

So long as the MAF isn't pegged you are okay. The thing is a stock MAF signal is programmed to an air flow that might exceed its limits with higher flowing intakes and heads. To understand you need to know how the MAF works. Simplified, voltage is applied to the MAF sensor to maintain a constant temperature of 200*F. As more air flows the sensor starts to cool and the computer increases the voltage to raise the temperature back to 200*F. If at maximum voltage the air flow cools the sensor below 200*F the MAF is pegged and the computer can no longer accurately calculate the air mass. Once this happens the AFR's become unpredictable and if the engine suddenly goes lean (and you are probably running WOT during this time) catastrophic events occur.

94Snake · Jan 5, 2013

The MAF becomes pegged after 5 volts doesn't it? That's what i was thinking but how does tuning becoming an issue with a stock MAF and bigger injectors. My tuner told me it didn't matter what my MAF was calibrated for because once he tuned it.......well it wouldn't matter.....i was trying to ask him questions about the settings while he was tuning and he wasn't talking lol.